This invention relates to a gauge or tool for determining the concentricity of a bore in a workpiece about a desired axis, and more particularly to a tool of this type which may simply and accurately determine when such a bore is off-center or eccentric and in the direction in which the axis of the bore is off-set.
In the manufacture of cylindrical bores in workpieces it is difficult to precisely determine whether the center of the bore is precisely located even if the bore is perfectly cylindrical. This is especially true in remanufacturing operations. For example, when an engine block is rebored, not only must the cylinders be precisely disposed but so too must the bore for the crankshaft and cam shaft. Merely reboring the hole truly cylindrical is insufficient; the axis of the hole must be accurately disposed or the parts when assembled may run eccentrically and wobble. The alignment of the axis of the center of the bore to obtain precise concentricity about the desired location is difficult and time consuming even for the most skilled machinist. To a large degree this involves experience and guess work or expensive jigs which precisely hold the workpiece and the boring tool. While such equipment may be cost effective when manufacturing the workpieces initially in large production operations, e.g., engine blocks, the cost for remanufacturing and for smaller quantities generally is not justified and if the precision is not obtained the work is scraped.
The prior art has not developed a satisfactory solution to this problem. In fact, the known prior art does not even appear to have directly addressed it. In none of the known prior art can the center of the bore be located so that a boring tool may be precisely located for boring or reboring the hole. Moreover, in none of the known prior art can a relatively inexperienced operator readily determine the position where the tool or the workpiece should be disposed for obtaining a bore concentric about a desired axis.
U.S. Pat. No. 2,883,758 of Zelnick proposes a device having four fingers spaced 90.degree. apart extending outwardly from the device and biased inwardly by springs so as to adjustably engage the wall of a bore to read variations in the radius thereof. In Zelnick there is a proposal to rotate the device through substantially 90.degree. after the fingers are moved into engagement with the walls of the bore. If the bore is symmetrical about its longitudinal axis, the tool can be rotated, otherwise not.
In Blankinship U.S. Pat. No. 4,530,161 pivotable spring biased feelers engage the bore of a pipe and the pivotal motion of the feelers are converted into linear positions which are converted into electrical signals.
In Mizuno et al. U.S. Pat. No. 4,288,924 the internal diameter of a bore is measured by levers which are initially squeezed together for insertion into the hole and biased outwardly to engage the wall of the hole, the position of the levers providing a reading of the diameter of the bore.
In Edouard et al. U.S. Pat. No. 4,186,494 bore dimension measurements are made by spring biased feelers disposed about a central frame, the feelers contacting the walls of the bore to be measured and the positions determined and converted into electrical signals.
In U.S. Pat. No. 4,251,921 of Fink a tool having caliper and collapsible arms independently extend and retract as the tool is pulled through a bore hole to log the variations in the bore hole.
In Jandera et al. U.S. Pat. No. 4,342,225 a plurality of pivoted arms engage the inside of a flexible member which engages the wall of a pipeline, movement of the arms signal variations in the pipeline bore size.
Price et al. U.S. Pat. No. 2,908,085 discloses an instrument for measuring the internal surface of a pipe or the like by means of feelers connected to position the core of differential transformers for obtaining the reading of the size of the bore.
In Koltgen U.S. Pat. No. 4,211,014 a bore inspecting gauge has radially extending pins which merely convert the position of the pins into a gauge reading to determine the diameter of the bore.